A damper is used to damp vibrations of, for example, a vehicle, a device, and a construction. For example, a damper disclosed in FIG. 3 in DE3018215A1 includes a cylinder, an annular rod guide, a rod, an annular oil seal, and an annular outer peripheral seal. The cylinder internally forms an action chamber. The rod guide is secured to an upper opening of this cylinder. The rod is inserted through an inside of the rod guide so as to be axially movable. The oil seal is installed to a lower side of the rod guide. The outer peripheral seal is fitted to an annular groove formed on an outer periphery of the rod guide. The oil seal seals an outer periphery of the rod. The outer peripheral seal seals between the rod guide and the cylinder. This prevents a fluid in the action chamber from leaking to an external air side.